Electron tube circuit



July 16, 1946. K. SCHLESINGER I ELECTRON TUBE CIRCUIT Filed May 11, 1943 10 Sheets-Sheet12 576N094 //VP(/ 7' FREQUENCY I WIT/l ,SUPPL V FREQUENCY CONSTO/VT Kgrtng ENToR ATTORNEY y 15, 1946- K. SCHLESINGER ELECTRON TUBE CIRCUIT Filed May 11, 1943 10 Sheets-Sheet 3 A TTOE/VEL July 16, 1946. K. SCHLESINGER ELECTRON TUBE CIRCUIT Filed may 11, 1943 i0 Sheets-Sheet 4 ATTORNEY Kn SCZHLESINGER ELECTRON TUBE CIRCUIT 1o Sheets-Sheet 5.

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ELECTRON TUBE CIRCUIT Filed May 11, 1943 10 Sheets-Sheet s July 16 1946. K. SCHLESINGER ELECTRON TUBE CIRCUIT Filed May 11, 1943 10 Sheets-Sheet 7 July 16, 1946. SCHLESINGER 2,403,955

ELECTRON TUBE CIRCUIT 230 4 226a Q22 I INVE/YTOP /6 KiurWes W ATTQPNEK July 16, 1946. K. SCHLESINGER ELECTRON TUBE CIRCUIT' Filed May 11, 1943 10 Sheets-Sheet 9 Q) G)v ,4 TTOP/VEK July 16, 1946. K. SCHLESING ER ELECTRON TUBE CIRCUIT Filed May 11,,1945 1o Sheets-Sheet 1o rg ua /N l/E N TO? KZu-JU bdZZw nger 7kg ATTORNEY Patented July 16, 1946 ELECTRON TUBE CIRCUIT Kurt Schlesinger, West Lafayette, Ind., assignor to Radio Corporation of America, a corporation of Delaware Application May 11, 1943, Serial No. 486,521

34 Claims. 1

The present invention is directed to electron tube apparatus. It is particularly concerned with circuit arrangements adapted primarily for amplification, although many other uses, which known types of amplifiers cannot fulfill, will be set forth by these specifications.

Such apparatus may be generally considered as involving a type of circuit incorporating a plurality of grid controlled rectifier tubes which, may be arranged in cascade and all of the tubes are condenser loaded. All of rectifier tubes of the cascade are so controlled as to operate in sequence. The circuit is so arranged that each rectifier has its grid or control electrode connected to the preceding condenser and the charge in the first condenser is repeated in all following condenser stages.

In. the system, the operational sequence, in its broadest sense, starts with the first tube and carries through to the last tube, with the total sequence time being substantially equally divided between the several tubes. The tubes may then be rendered operative in sequence by an appropriate distributor mechanism or, more conveniently, as will hereinafter be set forth, by an appropriate source of alternating current supplying operating voltages to the tubes to permit operation on the positive half cycles. With such operation, an indication at the last tube of the sequence will be the result of. some signal. control effective on the first tube of the sequence anumber of cycles of operation prior to the observance which. is equal to the total number of tubes in the sequence.

With this arrangement, the system may be considered as incorporating a plurality of tubes arranged in at least two groups by virtue of alternate connection of the anodes and cathodes of successive tubes of the cascade to the source of alternating current. In this way, the tubes of alternate groups? operate simultaneously in that all tubes whose anodes are connected instantaneously to receive the positive half cycle of the alternating current wave will b operative, while those tubes whose cathodes are connected to re- L ceive simultaneously this sam half of the alternating current wave will be inoperative. During the following half. cycle of the alternating current. the operation will be reversed, and. so on. In this way, the various tubes. may be considered as beingarranged in, at least two: groups with the tubes of alternate groups operating simultaneously. In connection with. the mod of operation hereinahove mentioned, it should. be pointed out that the tubes in the different groups operate simultaneously with regard to the energizing voltage, but that the signal wave passes through. the tubes sequentially. The division hereinabove made with regard to th two groups of tubes comes about by reason of the assumed A. C. operation. The operation essentially is sequential signal transfer from one stage to the next. succeeding stage, and so so. Within the meaning of the above explanation, the broad classification of groups will be understood in its generic sense and each group may thus include one or a plurality of tubes.

It accordingly is apparent that the circuit herein to be set forth operates with delayed outputs, in contrast to the practically simultaneous input and output of the usually known amplifiers. The present circuit operates, as will be seen, with linearly averaged effects of input control energy so that it may be used; as a D. C. amplifier as well as an A. C. voltmeter. In the latter case, it exhibits inherent selectivity and phase response which makes it readily adaptable to use as a locator or protective signalling device.

Generally speaking, the arrangement as it is set up is so constitutedv that the rectifying tube circuitsare grid controlled but operated with the plates or anodes supplied with alternating current voltages of predetermined and suitable frequency which. is, to some. extent at least, dependent upon the use to which the circuit is to be put. The tubes of the sequence have the cathode elements thereof alternately connected either to the positive or to the negative terminal of the A. C. supply energy source. The tubes are all connected so that the plates or anodes connect to the supply energy source through energy storage circuits, and each plate or anode connects directly to the grid or control electrode of the next tube. lhus, all tubes subquent to the first of the plurality are arranged so as to be controlled by an electrical charge accumulated by the preceding storage circuit which is charged under the initial control of energy flowing in the first tube. In the usual form, the storage circuits comprise primarily a condenser element which is shunted by a resistance or a correcting inductance element, which condenser is arranged to retain its charge for at least the period of the alternating current supply wave which supplies operating voltage to the tube plates or anodes.

Thus, it is an object of the present invention to provide a highly selective electronic amplifier operating in such a manner that the plates or anodes thereof are energized by an exciting alternating current of any desired frequency ranging, for instance, from that of the ordinary power supply lines or mains, for instance 56 or 60 cycles, to frequencies of ultra-high value.

Among th mor specific objects of my invention are those of providing an electronic amplifier arrangement; which particularly adapts itself for use in the detection of field strength variations, and particularly in an alternating current field having substantially the same frequency as that of the energy supply frequency.

A further object of the invention is to provide an electronic amplifier circuit particularly adapted for the production of single side-band trans mission systems.

Another object of the invention is that of providing an electronic tube circuit particularly adapted for the measurement of direct currents and direct voltages, and thus particularly useful in connection with photo-electric tube measurements, thermo-couple measurements, ionization and the like.

A further object of the invention is that of providing an electronic tube circuit particularly adapted for detecting magnetic or electrostatic field disturbances so that the tube circuit itself is capable of providing an indication of the actual location and distance of the point from which the disturbance was initiated. In addition, it is an object to develop a tube circuit which shall be capable of simultaneously indicating the source of a plurality of simultaneously occurring disturbances.

The system, in its preferred form, is not only capable of making measurements of the type hereinabove named, but is also so constituted as to be capable of reducing measurements of distance, elevation, thickness, pressure and the like to ones of capacity, inductance or resistance.

Still a further object of the invention is that of providing measuring apparatus particularly useful for making all types of alternating current measurements, such as inductance, capacity, resistance, voltage current, phase and the like. Also, the arrangement herein to be disclosed is generally capable of providing for making pH measurements and furthermore indicating the sign of the pH.

A still further object of this invention is to provide a circuit and apparatus for use in locating the presence or position of intruders in electro static or magnetic fields. In such arrangement, the system is particularly adapted for locating submarines, land and sea mines. airplanes in flight, and for use as collision prevention between airplanes, as well as for indicating the path of direction of motion of airplanes, motorcars and all forms of transports on land, sea and in the air.

A further object of the invention is to provide an electron tube circuit particularly adapted for measuring altitude or elevation, for instance, the elevation or altitude of airplanes relative to ground through an indication of the capacity changes between the airplane and ground. In this connection it may be pointed out that the system is, generally speaking, somewhat more sensitive in the region reasonably near ground, although it is generally useful, irrespective of the actual height from ground.

As a further object of the invention the system is to be designed for use in connection with the protection of buildings and for protection against when an object is moved within the field of the equipment.

A still further object of the invention is that of providing apparatus for use in geodetic work, and particularly for locating water, oil or ore.

A further object of the invention is that oi providing a system which does not alter its operational phase, and therefore, the number of stages of the amplifier is substantially immaterial, except for the degree of amplification desired and the sensitivity of response.

A further object of the invention is that of providing an electronic circuit arrangement which will function as a radio receiver with substantially constant band width no matter which of a plurality of carrier frequencies is received, and a further object of the invention in this connection is that of providing an audio amplifier with a substantially constant band width.

Other objects and advantages of the invention will immediately become apparent to those skilled in the art from a reading of the specification and the claims, taken in connection with the drawings, wherein,

Fig. 1 is a circuit diagram of a generalized form of the circuit of a two-stage amplifier;

Fig. 2 is a modification of the circuit of Fig. 1 provided with additional amplification stages;

Fig. 3 is a graphical analysis to indicate gen erally the principles upon which the system operates;

Figs. 4a, 4b, and 4c are a series of curves to indicate generally the phase and frequency responses of the systems of the character shown by Figs. 1 and 2, for instance, to indicate the possibilities of alternating current measurements;

Fig. 5 is a modification of circuit of Fig. 2 utilizing coupling circuits and alternating circuit bias;

Fig. 6 is a modification showing the general form of circuit of the preceding figures used in connection with a photocell;

Fig. '7 is a further modification showing the use of a circuit embodying the principles of preceding circuits in connection with alternating current measurements;

Fig. 8 is still a further modification of the circuit to show the use in connection with phase shifting measurements;

Fig. 9 is still another modification showing the use of the principles of the preceding circuits in connection with loss measurements;

Fig. 10 is a schematic representation of a circuit utilizing storage principles functioning as a speech amplifier:

Fig. 11 represents still another modification with inductive coupling;

Fig. 12 is a series of curves intended particularly to indicate the operation of the circuits of Figs. 10 and 11;

Fig. 13 indicates a protective system of the omnidirectional type;

Fig. 14. is intended to show the application of the circuits of the preceding figures used as an altimeter;

Fig. 15 is intended to indicate the use of the storage amplifier in the preceding figures in connection with a locating device;

Fig. 16 illustrates the storage amplifier used as a direction indicator;

Fig. 17 is a modification of the arrangement of Fig. 16;

Fig. 18 represents one form of the circuit used as a bi-directional electrostatic collision protection device;

Fig. 18a is a series of diagrams to indicate the iiesponse conditions of the indicating tube of Fig.

8; and,

but that the tube 2 Fig. 1-9 shows a. modification providing a different form of bias for the first stage.

Referring now to the drawings, and first to Fig. 1 thereof, there is shown a general circuit arrangement including only two tubes which will indicate substantially the general operational principles of the invention as above outlined. 'In the arrangement of Fig. 1, there are provided two separate thermionic tubes I and a which may be of any general and desired type, and which have herein been illustrated. schematically as tubes of the general triode type, although it is to be understood that any suitable multi-electrode tubes may be used with equalefiiciency.

In the output circuit of the tube I, there is provided a storag circuit comprising a condenser 3 and a resistance 4 which shunts the condenser. This parallel combination of resistance and capacity is connected, on the one hand, to the anode or plate 5 of the tube I, and, on the other hand, byway of the adjustable contactor 6 to a desired tapping point on a potentiometer 1. One terminal of the potentiometer connects to the oathode 8' of the tube I by way of the conductor 9 which is, in turn, connected to one end of the secondary winding ll! of a transformer II, and the other end of the potentiometer 1 connects by way of a conductor I2 to the opposite end terminal of the transformer secondary winding 10 and also to the cathode L3 of the tube 2- The control electrode 14 of the tube 2 is connected both to the plate or anode 5 of the tube I and to the condenser or storage element 3, and the plate or anode lb of the tube 2 connects to another storage circuit including the condenser IB and resistor 25, to one terminal of which an indicating element (assumed to be the meter t5) connects. The condenser of the storage circuit has its other terminal connected to the second terminal of the transformer secondary I0 through conductor 25, as does the cathode S-of tube I and the conductor 9.

Alternating current energy for energizing both of the tubes I and 2 is supplied to the transformer primary i9 by way of input terminals 20 upon which alternating current energy of any suitable frequency is impressed. Input signals which are to be amplified, for instance, are impressed by way of the input terminals '22 so as to be applied to the control electrode 23 of the tube I across the resistor 24 which connects at one end to the control electrode or grid 23 and at the other end to the cathode 8.

The system hereinabove described is believed to operate in the following manner:

Assume, for instance, that the alternating current energy applied through the transformer H is supplied so that the conductor I2 is positive with respect to ground (or conductor 25), and that the conductor .25., which supplies the anode voltage to the tube 2 and connects also to the cathod B of the tube I, is negative relative to conductor I2. It is apparent, under such circumstances, that the tube I will draw current wil1 be blocked because the cathode is of the tube 2 will be carried positive with respect to its plate or anode I5, but with regard to the tube I, the anode 5 will, by virtue of the application of the positive half cycle of alternating current wave impressed by the transformer i I, be carried positive relative to its cathode 8. Therefore, under this positive half of the alternating current wave impressed by the transformer II, the tube I will draw current. When tube 1 draws current, it will charge its plate condenser 3 in accordance with the emission within .6 the tube I. The current flow through tube I is. in turn, controlled by the average grid voltage existing during the half cycle of conduction as it appears across the grid leak resistor 24 as controlled by the impressed voltages at the input terminals 22. However, during the next half cycle of the alternating current energy impressed through the transformer secondary HI, it is apparent that opposite state will exist so that the conductor I2 will become negative relative to the conductor 25, and thus the anode or plate I5 of the tube 2 will become positive relative to cathode element I3. Accordingly, the charge impressed in the condenser 3 by virtue of the previous half cycle period of conductivity of the tube I will be measured by the tube 2 which now becomes conductive. It should be borne in'mind that the bias on grid I4 is constant (or approximately thereso) due to the fact that the time constant of circuit .3, '4 is long. This then provides a current flow into the storage condenser I6 which will be a measure of the charge of the preceding con denser 3. It will be appreciated that if a direct current is impressed at the terminal 22 it will appear amplified in the average plate current of tube 2, provided the time constant of the circuit comprising the condenser 3 and the resistor 4 is longer than, or at least equal to, the period of the alternating current wave supplied at the terminal points 20.

Normally, in the circuit hereina-bove disclosed, there is a direct current voltage drop across the resistor 4 which is due to the mean value of the plate current flowing from the tube I. This voltage drop normally would .block the tube 2, completely, unless it is compensated for by a suitable bias. It has been found, however, and is a feature of this invention, that the unblocking of the tube 2 may be effected by an alternating current voltage as well as by the direct current voltage, provided that the alternating current voltage is in the right phase with respect to the power supply of the second tube. Such conditions may be fulfilled by the use of the potentiometer l which is set to such a value that the plate current to the tube 2 assumes its mean value in accordance with the current flowing in the tube I. It is important to note that the A. C. voltage drop between the tapping point IS on potentiometer l and conductor I2 has the same effect .as would have an equivalent D. C. bias or battery between these points.

The two currents then change in the opposite sense, if the system is at balance under the control of an input signal voltage to be measured. Accordingly, it may be seen that the system described is capable not only of amplifying small value direct currents or direct current voltages impressed across the resistor 24, but also alternating currents or voltages, provided the frequency thereof is approximately that of the alternating current energy source connected at 20 and the beat note (if resulting) is at least in the response range of the storage circuit, as will later be set forth in further detail.

Referring now to the arrangement of Fig. 2, it will be understood that like parts are referred to by like numerals in this figure, as in all others. The arrangement of the circuit in Fig. .2 is essen tially similar to that hereinabove described in connection with Fig. 1, except that the arrangement is used as a multi-stage amplifying device. In the arrangement of 1, each stage, such as the tube 2, has its own voltage divider I which adjusts its operational bias to optimum conditions. If more stages are added with the circuit of Fig. 1, each subsequent stage must be separately biased. Since subsequent stages depend upon the preceding stages, diificulties are present which increase with the number of stages, To overcome such difficulties, a self-biasing system is shown by Fig. 2. With the arrangement of Fig. 2, provision is made whereby appropriate bias is applied only to the first tube I of the series and the remaining tubes 2, 39, 40 and so on function as self-biasing devices.

From the foregoing, it will be appreciated that any changes of control signal energy applied to the input terminals will be first observed in the output indicator circuit I6, 2I and at the output terminals I1 and I8 (or the indicating device 65) at a time n/2 cycles of the supply A. C. later, where n represents the number of stages in the system. This permits a ready control of transit time of signals through the system by a variation of the frequency of the A. C. power supplied at power input terminals 20, and thus serves to adapt the system to certain of the uses above stated and explained further in what is to follow.

Considering now Fig. 2, it will be seen that no individual bias control has been provided for any of the stages, except for the first one, which is denoted by resistor 3| and potentiometer 30. Even despite the absence of individual controls, all stages may be made to draw equal amounts of average emission, i. e., all stages may be made to operate under equal conditions if only the first stage is adjusted separately and critically, for example, by the potentiometer 30.

To show this, it may be assumed that the first stage I is permitted to draw a particularly strong emission, under the influence of a strong positive control signal at any instant. Then, there will be an unusually strong negative residual charge across its plate condenser 3 which, during the next half cycle, now acts as grid bias for the next valve in the connection shown. The second tube 2 of the system may thereby be completely out off during its supposedly conducting half-cycle, which follows. This, in turn, results in zero charge across condenser 33 and therefore is zero bias for the next stage 39. This third stage, therefore, produces a strong and blocking bias for the fourth stage, and so forth.

It will be apparent, therefore, that the average emission and charges of the first, third and fifth stages, and so forth, are strong, but of the second, fourth and sixth are zero.

The opposite distribution would hold, if the first stage had been less conductive or even blocked off, by a strong negative signal, at the time of its supposedly conductive half-cycle.

It is, therefore, possible to bring the entire system into a condition of balance, where all stages draw equal average emissions and operate under equal conditions, simply by setting a critical medium average emission in the first tube I. With any given input signal, this can be done by applying an appropriate bias to the cathode B of first tube I. As outlined before, this may be either a D. C. bias, an equivalent cophaseal A, C. bias, or a rectified A. C. bias, as disclosed later herein in connection with Fig. 19. The latter is shown in Fig. 2. as derived from the common A. C. supply by an ohmic voltage divider consisting of resistor 3I and potentiometer 30. With the help of this system, the entire system may be brought into balanced condition and the output indicator 65 to center-scale.

This operation will be more particularly understood by reference later to be made to the diagram of Fig. 3. At present, is will be seen that the tube I has appropriate A. C. bias applied by way of the resistor 3| and potentiometer 3B which has its center tap connected by way of the conductor 32 to the cathode element 8 of the first tube I. The bias arrangement provided by the potentiometer and its variable tap 6 (see Fig. 1. for example) between each stage is avoided, and only the first tube of the series is maintained at a manually adjusted. bias level in Fig. 2. If, under such circumstances, input signals are applied, as in Fig. 1, to the input terminals 22, they now affect the control grid 23 of the tube I and function to control the current flowing therethrough, and thus determine the charging of the condenser 3, as explained in connection with Fig. 1. In the arrangement of Fig. 2, however, it will be seen that the tube 2, representing the second tube in the series, now functions to draw current at times when the tube I is blocked. In this Way, the condenser 33 of the condenser and resistance network 33 and 34 is then charged under the control of the storage voltage of the first storage circuit 3, 4, and consequently, the third tube 39 in the series will be conductive at the same time as the first tube. The bias on tube 39 is constant and determined by the slow discharge of the storage condenser 33 through its shunt resistor 34, which discharge is negligible (as was discharge from condenser 3) during a half cycle of the A. C. at the terminals 20. At times when tube 2 ceases to draw plate current, it is apparent that the tube 39, that is, the tube illustrated as the third in sequence, will draw plate current and tend to charge the condenser element 43 of the condenser and resistance combination 43 and 44. It then happens that the operation is such that the charge is next transferred at the fourth half-cycle by tube 40 into its storage circuit and the rest of the operation naturally follows accordingly.

Alternating current voltages are applied as the plate voltages for all of the tubes of the series, with the alternating current energy connected at the power input terminal 20 and then through the wingings I9 and ID of the input transformer II, so that the tubes I, 39 and 4|, respectively, have their plate circuits energized by alternating current energy flowing in the conductor I2 and controlled by the stabilizer resistance 46, while the tubes 2, 40 and 42, for instance, have alternating current potentials applied thereto by way of the conductor 25.

If now, particular reference is made to Fig. 3, it will be seen that there is plotted a schematic representation of the effective grid bias on the first tube I as the abscissae with resulting plate current indicated as the ordinate. If now, it be assumed that the tube I cuts off at some value of its grid bias indicated by point a, then various plate currents will flow through the tube for all values of grid bias between that indicated at a and zero bias, which may conveniently be represented by the line drawn between point a and point I) on the curve (and marked Tube 1) which is the rectifier characteristic of the stage with A. C. power supply. Point b in this instance will represent some current which will flow through the tube I for zero bias, which conventionally may be represented as current Io.

It was above explained that at times when no avera e current flowed through the tube I, the storage voltages appearing in the condenser 3 are zero and, consequently, under such circumstances, the tube 2 draws a current In which is represented by the value c. This current in tube v2 will decrease as the average current in tube I increases. This current in tube 2 will become zero when the average voltage drop across the first storage circuit is equal to cutoff (that is, oa). The critical first stage current to bring about such a condition (cutoff voltage) is readily found from Fig. 3 by reference to the Load line which is drawn through the original at an angle B where the tangent of the angle B is equal to the value of resistance 4. This Load line indicates the cutoff value of primary current (I0) where it intersects the current ordinate ac at point 1.

It will be appreciated that the value of bias on tube 1 necessary to provide cutoff in the sec 0nd tube 2 will be that value c which is represented by the point at which the first tube has a current Ic. Thus, whenever tube 1 draws a current equal to (or greater than) 10, tube 2 is cut ofi. This happens at point (2 and the appropriate bias for the first stage is found at point e, beneath d. Hence, the overall characteristic for two stages is represented by the line c-e.

Likewise, following the same analysis, it is apparent that the next point for cutofi in tube 39 (the third tube) is readily found to be at the point a, while the point at which maximum current flows through the tube 39 is found to be at point it. From what has been stated, the overall characteristic over three stages may be assumed to be represented as that line which is drawn between points 9 and h.

It is now apparent that all of the characteristics conventionally represented for the tubes 2 and 39 pass through, or approximately through, some common point 8. where all stages pass equal current after a condition of bias is established on tube l, which can be brought about by the bias value represented by the point t, which is the bias applied to the first stage to provide this equilibrium condition.

It can be seen now that the tubes of the sequence have gradually steeper overall characteristics, with the last of a series of n tubes being the steepest, and which, for instance, might be represented by the characteristic m, m, s, 1;, w. It thus becomes apparent that the increase in slope in the overall characteristic, which is desired from the standpoint of amplification, is balanced against the decrease in the range of applied bias voltages, such as e, y, as compared to a value 0, a of grid bias on the first tube above. However, for control bias within the range between values represented at points 9 and e, amplification may take place with extremely high undistorted gain due to the steepness of the overall characteristic represented conventionally by the curve m, :c, s, v, w.

In the foregoing description,' reference was made particularly in connection with Fig. 3 to an explanation of the operation of the circuits of Figs. 1 and 2, where the system was assumed to be controlled by a constant voltage or D. C.

signal applied to the first tube of the system, that is, tube 1, to control the resultant output of the system and consequently to provide amplification of that voltage at'the output terminals l1 and. i8. functioning under certain conditions equally well under the control of applied alternating current signals on the input terminals 22. To this end, Fig. 4 will explain how A. C. observations are achieved.

The system, however, is capable of terminals 2!].

.10 If reference be made now to the several curves of Fig. 4, it can be seen from curves of Fig. 4a

that the alternating current supply frequency is represented by a sinusoidal voltage wave designated by the solid line Es which is of a frequency represented by fs. If now, -a condition be assumed where the controlling signal voltage shown by the dot-dash line Ei impressed upon the input terminals .22 is of a like frequency and in phase exactly with the supply frequency Es (as impressed upon ithe .power terminals 29) then it can be seen that the plate current in the first stage has the vfor-m shown by curve 'Ip, (dashdouble-dot line) in Fig. 4a. Since current does .not flow through the tube 1 for half of the cycle of the supply voltage Es appearing at the terminals 2%], :it is apparent that the instantaneous current flowing through the tube l for the negative half-cycle will be zero, as is indicated, notwithstanding the fact that the impressed voltage E is applied to the input terminals 22 for the full duration. The plate current 1 is not directly observed, but the output measurement is directly proportional to the charge which this current produces in the first storage condenser -3 and is thus represented by the shaded area marked Average current. Where a cophaseal state of supply and signal voltages exists, then this shaded area, and hence the output reading, is a maximum, because the signal grid voltage E1 is positive during the conductive period.

A condition may now be assumed where the signal voltage E1 is again of the same frequency is as the power supply voltage but out-ofphase at the terminals 22 with regard to the power supply voltage Es supplied at power input These conditions are graphically represented by the curves of Fig. 4b. In this case, the instantaneous current flowing through the tube I of the system is represented by the dot-dash line I'pl. It is of reduced magnitude relative to the current represented by Ipl in Fig. ea .for a cophaseal case, because the signal grid voltage E1 is now negative during the conductive period. Accordingly, the output indicator-reading, which measures the area shaded under the curve I' i (that is, the charge across storage condenser 3 is smaller than was indicated in Fig. 4a and can become Zero in some extreme cases of strong negative signal input.

The foregoing is illustrative of the fact that the storage device is responsive to A. C. signal inputs, provided that they are of the same frequency as its supply. These principles thus become the basis of operation of the storage principle circuits shown and described in the remaining figures of the application.

The foregoing considerations apply to conditions where the signal and supply frequencies are equal. If the supply frequency is given, the systern does not respond to any arbitrary frequencies but rather only to discrete frequencies. The circumstances for such spectral response are shown by Fig. 4c. The system responds best (greatest sensitivity) to all frequencies which are an integral multiple of the supply frequency, with 1 1 tion, the response of the storage amplifier for various conditions for various frequencies of signal input relative to the power supply frequency is shown. It is apparent from Fig. 4c that the amplifier is selective.

It was above shown that the system responds both to direct current signals and to alternating current signals of the same frequency as the supply. With reference to curve of Fig. 40, conditions may be seen where the amplifier also responds to different frequency values selectively, where such frequencies extend from zero frequency or direct current to extremely high frequencies and hear an integral relationship with regard to the energizing frequencies supplied at the power terminals 20. If, for instance, the amplifier is excited by direct current applied at the terminals 22, then the response range is that indicated with a maximum at 100% on the curve and included within the shaded response area. The band width covered within the shaded area is given by the time constant chosen for the storage circuit comprising, for instance, the condenser 3 and resistor 4, or for instance, the con.-

denser 33 and resistor 34, and so on. If now, the i impressed signal frequency which is applied to input terminals 22 happens to coincide with the supply frequency at the power terminals 20, then a response, such. as that indicated at the point where the signal input frequency is equal to is, that is, the supply frequency, will result. Another maximum is observed where the energizing signal frequency is twice the supply frequency, although this second-order response will be reduced from that condition where the supply fre- I quency and impressed signal frequency are equal. The response range or band width is the same for all conditions, but the gain is reduced at the signal frequenc 2fs to about 33% from the first order response, as indicated by the curve. if the impressed signal frequency is three times the value of the supplied frequency, the response will be about that which resulted with direct current being supplied as the control signal energy, as, for instance, for still higher orders.

Accordingly, it is evident from the curves of Fig. that the amplifier band width is, in each instance, the same, but the sensitivity is reduced with increasing signal frequency. It is also evident that if the signal frequency is other than some integral of the supply frequency, the amplifier will not respond and the amplifier is found therefore to be selective as to the control signal input. However, the amplifier will respond to beat frequencies which fall within the shaded areas or regions of Fig. 40. It thus becomes apparent also that since the amplifier does not respond to impressed frequency values intermediate multiples of the supply frequency the amplifier does not pick up static or noise occurring within these ranges and shows a high signal to noise ratio performance.

The general curve showing the sensitivity for various signal frequencies at given supply frequency is that shown in Fig. 40 by dash lines connecting the peaks of selective signal response at the various frequency values, and it can be shown that this is a hyperbola which follows the general formfrequency fed into the system at the terminals 20 to power it.

Likewise,

In Fig. 5, a further modification of the arrangement of Fig. 2 has been illustrated. In this arrangement, the signalling energy is impressed, as in Fig. 2, across the input resistor 24 by way of the output energy derived from a suitable load line or cable 50, so that tube I has its control electrode 23 energized in the manner hereinabove explained in order to produce the mentioned charge in the condenser 3 of the time constant circuit comprising the condenser 3 and the resistor 4 connected to the plate or anode element 5 of the tube I. The time constant circuit comprising the condenser 3 and the resistor 4 is of the order hereinabcve explained and the operation is essentially like that described in connection with Fig. 2. However, in the circuit of Fig. 5, additional stabilizing resistors 52 may be included between the various stages of the system, as indicated. With the arrangement shown, two additional stages 53 and 54 have been added in order to be able to arrange the system in groups of twin tubes to use twin triodes with the heaters coordinated in pairs.

In cases where the system is energized from alternating current voltages, it is desirable to make connection from the cathode elements of the tubes to the conductors I2 and 25, as indicated, and consequently, separate heater current paths are provided for each half of the tubes by way of the connections through the coupling transformer windings 56 and 51 respectively. Also, in the arrangement of Fig. 5, provision has been made whereby various tubes may be combined within a common envelope and, to this end, for instance, tubes I and 39 may be combined within a single envelope, likewise tubes 2 and 40, also tubes 4i and 53. and 42 and 54. This is always possible where the total number of stages is an integral multiple of four.

Since the gain from the system is extremely high, and since extremely high gain, as would be indicated by the curves of Fig. 3, is very difficult to control, it is desirable that some degeneration be provided within the system which can be achieved by means of cathode degenerative resistors 55 indicated. Since the system herein dis-- closed is sensitive to alternating current excitation, it is particularly important that suitable shielding thereof be provided in all instances. To this end, the shieldin member 69 forms a housing about the complete instrumentality and all cathode elements and leads, and one side of the system is grounded, for instance, by the conductor 25 connecting at point 6| which would provide the ground of the heater of the first tube I of the system. It is also important that the conductor 50 supplying the control voltages to the grid or control electrode 23 of the first tube I, have suitable shielding which is conventionally indicated by shield 62. Likewise, in order to avoid any electrostatic coupling between the primary winding I9 and transformer I I into the secondary thereof, a grounded electrostatic shield means, indicated at 63, as is well known, is provided. In this way, the amplifier is completely insulated from external and extraneous undesired controls, and stabilization against disturbing influence thereon is provided. The excitation and resultant output, as it appears at the output terminals I1 and I8, and, for instance, is conventionally represented as influencing the meter 65, is due entirely to the control signal voltages applied upon the system by way of the input conductor 50 rather than external disturbing influences.

In the arrangements of Figs. 6 to 9, further modifications of the system have been illustrated where the storage amplifier system is used under the influence of signal input of the same frequency as its own supply. In Fig. 6, the control is by way of a photo'tube which is energized by the common supply transformer and activated by eX- ternal light directed thereupon. In the arrangement of Fig. '6, the phototube output is always in phase with the supply voltage wave. In the arrangements of all of Figs. '6 through 9, the signal frequency coincides with the supply frequency. As to its phase, the signal frequency and supply frequency coincide in the photo-amplifier modification of Fig. 6, while the devices of Figs. '7 to 9 are inherently out-of-phase, but phase shift is measured by the act of bringing about a cophasal condition of operation and observing maximum output.

With the arrangement of Fig. 6, the overall sensitivity of the system is large and, therefore, provision has been'made byway of a, variable resistance element 6'', replacing the input resistor 24 of the arrangements of Figs. land 2, for instance, for reducing the impressed voltages which are applied to the control electrode 23 of the first tube I of the system under the influence oi strong illumination. In the modification of Fig. 6, the complete system is housed within the electrostatic shield means 63 .in which is included a window member 68 through which light from an .external source is directed upon the phototube member 69 contained within the housing. The window 68, if desired, may include a lens arrangement so as to focus sharply light which is to control the photoelectric current flowing in the phototube 63, thus .to vary the control potential on the control electrode .23 of the first tube I of the system.

In the arrangement shown, the cathode heater oi the cathode of tube vl is connected to the shield at point '6 l, asin the arrangement of Fig. 5. The heater elements are arranged in groups and are separately energized by two heater coils 56, which are, in turn, connected to either of the two terminals of the secondary of the power transformer ll. Such connections avoid insulation troubles.

The phototube 69 is so'connected that the anode element H thereof connects to the conductor l2 and is supplied with alternating current in the same manner as the plateor anode 5 of the tube I, so that, at times when the plate or anode 5 of tube 1 is supplied with energy of the positive half-cycle of the alternating current source connected at the input terminals 20, the anode H of the phototube will also be positive, and then light entering upon the phototube 69 to influence the photoelectric cathode element 12 thereof will provide an A. C. voltage .drop across the input resistor 61 to-give a positive swing on the grid or control electrode 23. The input resistor 61 is variable, so that the overall sensitivity may be readilyadjusted.

The time constant of all storage circuits 3, 4, etc., is made large as compared to the supply as was outlined in what is said above. Suitable A. C. bias for the first stage of the system is applied in the same manner shown in connection with the arrangement of Fig. 2.

The amplifieriof this system preferably has an odd number of stages since then the output increases with illumination on the phototube 6s.

The A. C. bias is set on the first stage by the slider of potentiometer 30, so that the bias on the last stage 39 is at cutofi, which permits an indicator 65 of higher sensitivity to be used.

However, if the system is somewhat non-linear for small light fluxes, the operation may be improved by providing five stages (as hereinabove indicated in other circuits) and securing the desired linearity by providing cathode degeneration in each of the stages, Under such circumstances, as disclosed by Fig. 5, the use of cathode resistors tends to straighten the characteristic. Thus, five stages, with degeneration, provide the same photosensitivity as did the three stages, but linearity is improved.

Still another application of the invention is shown in the circuit arrangement of Fig. '7, wherespecial provisions have been .made for use of the device for alternating current measurements. In the arrangement shown, the energy supplied at the supply input terminals 213 is now fed through a transformer '55 which has a split secondary winding consisting of the secondary turns 16 and it, respectively, with the center tap 18 connected to a ground point 19, as indicated, which point coincides with the connection to ground of the cathodes ofthe first and third tubes l and 39 respectively of the system. Alternating current voltages are supplied to the plate electrode members of the tubes i and 39 by way of the conductor i2, as described, ioriinstance, in connection with Figs. 1 and 2, and the plate of the second tube 2 is grounded through the conductor 25.

In order to provide for making alternating current measurements, a phase shifting network, comprising the series arrangement of the capacity element as and the variable resistor 81, is connected between the outside terminal points of the two secondary windings it and H, whereby, through adjustment of one of the elements and 81, varying phase shifts may be provided between point 8 2 and ground 19 without changing the voltage between point 82 and ground 19. At point 82 the unknown impedance 83 is connected serially to ground i9 through switch 84 with the variable grid resistor 61 which is accurately calibrated. In this way, when voltages appear .at the'point 82, they are applied through the unknown impedance 83 and switch 84 to the grid or control electrode 23 of the tube 1 to control the current flowing through the tube 1 in the manner ,hereinabove explained.

In the operation of this system, the A. C. bias is adjustable by potentiometer iii! to a value Where a cutoff condition holds on tube 39 and meter .65 is at zero reading where the switch 84 is open (as shown). Now, switch 84 may be closed and the A. C. signal transferred from transformer I5is impressed .on thegrid 23 of tube 1 through the phase shifting network 80, 8i and the unknown impedance 83 in anarnplitude which depends upon .andIis proportional to the value of the grid resistance 61. With this condition, the grid resistance iii is adjusted until an indication just appears on indicator 55. The phase control 8i is now adjusted and, in the general case, the indication on the device 65 will go through a maximum and, when the maximum is reached, the cophasal condition of grid input voltage and supply voltage is obtained. This permits observation and determination of the phase angle of the unknown impedance 83 which coincides with that produced between elements till and 8| and is of opposite sign to that of the elements Bil and BI. To ascertain the exact value of the unknown impedance 83, the phase condition above set by element '8! is maintained and the 15 value of the grid resistor 81 is reduced until the indication on 65 just disappears and then the unknown impedance can be calculated from the value of resistance 61 by voltage divider formulae. In this operation, the current flow in the outer circuit 80, BI, TI and I6 is relatively large compared to the current flow through the unknown impedance 83 to ground I9 through the resistor 6! and, further, the grid impedance G1 is a small fraction of the impedance 83, which 1 condition is always met with a sensitive amplifier.

Figs. 8 and 9 are modifications of what is shown in general form by Fig. '7. Figs. 8 and 9 are related to a showing for measurements of technical inductances and capacitors, respectively, with losses. The general technique is like that explained in connection with Fig. 7, except that the push-pull transformer secondary I6, 11 is no longer required due to limited phase shift to be expected. In each of the arrangements of Figs. 8 and 9, the unknown phase shift may be ascertained from the phase retarding network comprising the resistor 85 and the capacitor 86. The resistor 85 is connected in the A. C. supply lead I2 and the capacitor connects to ground SI from point 90 which constitutes the junction point of connection of the network elements 85, 85. The calibrated resistance element 8'! enables the value of the inductance 88 Or capacitor 93 to be ascer- I tained. In the case of the inductance measurement, the inductance 88 is connected between the grid 23 of tube I and ground 9|, while the capacity element 93 will be connected between the grid 23 and the phase delayed plate supply for the tube I. With the circuits of Figs. 8 and 9, the adjustment of elements 85 and 8B of the phase shifting network generally is of a closely related nature to the phase shift adjustment of elements 80 and 8| in Fig. '7. Likewise, adjustment of resistor 81 is for substantially the same purpose as the adjustment of resistor 61 in Fig. 7.

As in some of the preceding circuits, with the systems of Figs. 8 and 9 it will be appreciated that tubes I and 2 may be combined in a single envelope by using tubes of the general types of the 6E8 and 6J5 for instance.

In the modification shown by Fig. 10, provision has been made to use the principle of the circuits hereinabove explained in connection with speech transmission, as contrasted with the general type of measuring instrumentality. In the arrangements particularly disclosed in the preceding figures, it was assumed that the control signal is direct voltage or a constant amplitude alternatr ing current voltage. Under such circumstances, the time constants of the storage circuits comprising, for instance, the charging resistor 4 and the storage condenser 3 connected to receive the output from tube I, can be made relatively long. However, in arrangements where the signal energy is such that the signal strength varies, as will be the case to be considered in the description of Fig. 10, certain modifications must be made in the system. For instance, the supply frequency which is to energize the plate or anode elements of the various tubes will have to be of a relatively high frequency value and at least twice as great, and preferably more, as the highest signal frequency which is to be supplied to vary the input for amplification. For instance, for speech amplification the frequency of the supply energy which is to energize the plates of the various tubes of the system must now be in the higher frequency range and preferably of the order of 20 kc. or more.

Even if the supply frequency chosen is high, the system of Fig. 2, for instance, will not handle audio control signals because of the high inertia of the storage circuits. Accordingly, the storage circuits which had a relatively long time constant in the examples heretofore discussed, must now be so designed that they have an extremely short time constant, which is preferably less than (and certainly no greater than) the shortest period occurring in the signal input, meaning the period of highest frequency which is contained in the signal input to the system. If, for instance, it were assumed that the system of Fig. 10 were to be used as an amplifying arrangement for amplifying audio voltage signal input energy and a high fidelity system were to be desired, then it will be apparent that the time constant of the storage circuits of each of the tubes should be shorter than 30 micro-seconds, since the system should function properly up to sound frequencies of the order of 10 kc., and the supply frequency then should preferably be of the order of 30 kc. or higher.

For these conditions, the circuit shown by Fig. 0 is such that energy of a relatively high frequency, as above explained, is developed at the power supply I00 and fed through the transformer IUI to energize the conductors I2 and 25, as above explained. The control signal voltage which now may be audio frequencies ranging from zero to 10 kc., may now be applied to the input terminals I03 and I04 and fed through transformer I05 to be applied upon the control electrode 23 of the first amplifier tube I.

Since the system herein disclosed may amplify audio frequency directly, or the system may function as its own demodulator, it is possible to supply the audio frequency signals as modulations upon a radio frequency carrier which is impressed at the terminals I03 and I04. Under the c0nditions where the audio frequencies are applied as modulations of a carrier frequency, the secondary winding IIG of the transformer I05 (which, in this case, is a radio frequency transformer and is contrasted to audio frequency transformer where the signals do not appear as modulations of a, carrier) is now preferably tuned by means of the condenser II'I, but it will be understood that the condenser may be omitted in the case that the signals are supplied without being modulations of a carrier frequency.

In the arrangement shown in Fig. 10, it is to be understood that any desired number of stages may be utilized, although only four stages have been shown. Under explained conditions, with fairly extremely high supply frequencies (for instance, 30 kc. as at the source I00) and very short storage inertia, the charges across the storage condenser circuit are able to follow even the fastest rate of change of the input signal and are therefore transferred through the complete system and amplified in each stage until they appear at the last storage circuit I I8 with a delay n 1 seconds (n=number of stages and 30 kc. is the assumed supply frequency) but otherwise undistorted. It is thus evident that the delay period is a function of the supply frequency, so that it is subject to control by varying the supply frequency and thus can be made shorter by increasing the supply frequency, although no changes are made in the 17 storage circuits or their time constants and the quality of the reproduction suffers no change. This system, therefore, is of the type well suited to use as a reverberation control.

The output energy which appears across the last storage condenser H8 is supplied to a sound reproducing element I I9 by way of the transformer coupling I26 connected across the storage condenser.

If reference is made at the moment to the curves of Fig. 12, it will be seen that the frequency response of a circuit of the type of Fig. 10 is generally indicated by the curve a of Fig.- 1-2. This curve a shows that the frequency response plotted against the signal frequency impressed (with the assumption that the supply frequency for the tube anodes remains constant) falls off rather rapidly with increases in input signal frequency.

Accordingly, to improve the response, reference may now be had to a further modification of the circuit as shown by Fig. 11. In the circuit arrangement of 11, the same supply frequency as above from the source 160 is again fed through the transformer IQI to energize the plates of the various tubes of the system by way of the conductors I2 and 25, as already explained. Incidentally, in order to provide suitable alternating current bias on the system, provision is made for the use 'of the series condensers I28 and I29 serving as a capacitive voltage divider to replace the resistive voltage divider of Fig. 10. Nevertheless, previously described bias supplies may be used at this point.

With the bias system shown, provision is made for connecting a suitable high frequency choke I36 between the cathode element '8 of tube I and the conductor 25 to avoid the detrimental effect of the cathode to ground distributed capacity, represented at PM in Fig. 10.

In order that the high frequency response of Fig. 11 shall "be improved over that of Fig. 10, the storage condenser has been split into two parts 3' and I33, and an inductance element I3! has been interconnected and placed between the two condensers '3 and I33. For low signal frequencies, the coil or inductance I3! can be neglected and the storage circuit acts as in Fig. '10, but for high frequencies, series resonance occurs between inductance 'ISI 'and'capac'itor I33 which results in a peakingeifect for high audio frequencies. This, then, produces the improved response shown "by curve 2; of Fig. 12. The inductance element 'I3I thus serves as a peaking element, and the time constant of the circuit, "comprising the capacity I33 and the inductance I3I, which for low audio frequencies is the same as that represented by the capacity 3 and resistor I in Fig. l0,appears to be reduced for high audio frequencies by Way of insertion of the series peaking inductance I3I and the response curve of the system broadens out, as indicated by curve I) of Fig. 12, during a-greater portion of the frequency band, although the response drops off more rapidly as extremely high audio frequencies of the range are approached. Similar time constants and series peaking inductances are provided in the remaining stages of the system for like purposes, and hence require no further explanation. Here again, the number of tubes or stages may be increased without departing from the spirit and scope of what has been illustrated.

Reference may now be made to the circuit shown by all the Figs. 13 through 18 for further 18- adaptations and uses of the principles disclosed heretofore.

In the arrangements of Figs. 13 to 18, application of the storage principle will be disclosed in a field broadly termed protective or locating systems. The common features of all of these 'circuits is that an alternating magnetic or electrostatic field is set up in space which oscillates at the same frequency as the storage amplifier connected to the field electrodes. The system is so balanced that as long as the field is undisturbed the output indicator of the storage system is at equilibrium. As soon as any variation of the 'field distribution in space occurs, for instance by the intrusion of a conductive, dielectric, or ferromagnetic body or object, the particular property of the storage principle makes it possible to indicate that change in the field, not only in magnitude but also in a directional manner. "Thus, not only the presence and distance of an object, but even the location thereof, is discernible.

In the arrangement particularly shown by 13, there has been disclosed what may be termed an om-ni-directional indicating or protective system, whereby the presence of any object, whether it be conductive or dielectric, which would tend to disturb the fieid equilibrium may be observed and indicated equally well in all directions of a plane. In this arrangement, the supply frequency energy, which may be of any suitable value, is developed by a source of A.'C.energy I50. This source of energy [59 serves in connection with the arrangement of Fig. 13 not only to supply the activating energy for energizing the plates of the several tubes of the storage amplifier system 1300, as was explained in the arrangement of the figures heretofore discussed, but it also serves, as will be more particularly pointed out later, as the activating energy source to produce an electrostatic field 30! in space. The produced =electrostatic field may be modified through the presence of any object 'II 'fl within the field tending todisturb a normally balanced condition. When such motion occurs, a change in the energy transfer from the source of supply frequency I50 "to the input to control the amplifier will be 'in'dicated, as will be explained in what follows.

In the arrangement disclosed, the supplyfrequency energy from the source I50 is now fed by way of the conducting leads 152 and transformer I5I to energize the plates or anodes of the several tubes of the storage amplifier 300 by way of the conductors I2 and :25, in a manner heretofore explained. At the same time, energy from the source I53 is fed by way of an additional pair of conductors I 53 to a primary winding I54 of a high voltage transformer I55 from the secondary I56 of which a substantialamount of energy at high voltages is derived and caused to produce a strong electrostatic field (for instance represented by between a suitable field electrode element .451, such as an antenna or the equivalent, and ground I58. The voltage between the antenna element I51 and ground may be represented, for convenience, as Es, and th capacity between the antennaand ground may be indicated conventionally by the capacity element shown in dotted outline as the capacity I59.

In order to provide the voltage Es on theelement I51, the high voltage step-up transformer I55 has been provided with a split secondary winding at which the midpoint I50 connects b y way of the conductor I6I to the grid or control electrode 23 of the first amplifier tube I of the system. The upper half of the split secondary I56 connects at its outer end by way of conductor I 52 to the antenna element I51, while the lower end of the split secondary connects through the parallel condenser combination comprising the condensers I63 and I64 to ground at I58. Under such circumstances, th arrangement disclosed provides a bridge structure with the center tapping point I60 at an A. C. potential relative to ground which can be adjusted, and even made zero, by the condensers I63 and I64. If the bridge condensers I63, I84 are equal to the antenna capacity I58, the center tap IE is at ground potential. If, however, the bridge condensers are set to be larger or smaller than the antenna capacity, the center tap voltage is either opposite or cophasal to the amplifier supply voltage and increases with the unbalance. Consequently, an adjustment of I63 can be found Where the output meter 65 reads exactly center scale, so that a conductive grounded body I18 increases the output reading on indicator 65 while a dielectric body causes a decrease in the meter reading.

Referring back to Fig. 4b, the curve E1 showed an out-of-phase relationship relative to the supply voltage E3. The adjustment herein made is of substantially the same general character. To achieve the balanced state represented by a center scale reading of indicator 65, the condenser combination I63 and IE4 is preferably adjusted substantially so as to balance the capacity I59 as representing the capacity between the antenna or other element I51 and ground. This adjustment is very critical and is provided by a coarse control, in the form of a large condenser I63, and a fine control in the form of a small condenser I64. Such an adjustment is preferably facilitated by pro-setting once for all the larger of the condensers I63 and I64 and then leaving that condenser substantially fixed, after which time the smaller condenser I64 may be varied slightly to obtain balance. Generally speaking, the voltage developed across the complete secondary winding I56 is equal to twice the voltage applied to the antenna element I51 relative to ground. In order to protect against possible touching of the antenna element I51 or its leadin I62, a suitable resistance element I66 may be provided. Likewise, in order to protect the storage amplifier system 380 against overload, a protective resistance I61 is included in the lead between the center point I60 and the control electrode 23.

If now the conditions hereinabove explained are such that in the absence of any change in the capacity between the antenna element I51 and ground I58, a substantially balanced state is continuously obtained, then a center scale reading is registered on the final output indicating device 65. However, if now there comes within the field produced between the antenna element I51 and ground I58 some object, such as that conventionally represented at I10, which would tend to disturb the field, the condition of balance heretofore achieved by way of adjustment obtained by way of condensers I63 and I64 is disturbed. The result is that the potential at the point I60 relative to ground I58 will change and an indication, as above indicated, will be produced on the output meter 65. The voltage disturbance at the bridge point I60, which would result from any body, such as that indicated at I18, coming within the field of the antenna or other element I51, might be expressed by the following formula:

Where ex represents the voltage between the bridge balance point I66 and ground I58;

Es represents the voltage between the antenna and ground;

Cs represents the capacity of the antenna I51 to ground I58;

it represents the height of the antenna I51 relative to ground I58;

a is the radius of the sphere or body I18 which is tending to cause the unbalanced condition; and,

r is the distance of the body I10 from the antenna Under such conditions, it will be seen that the reaching effects, and thus the efilciency of the system, fall off as the sixth power of the distance of the object tending to disturb the balanced field. Under such circumstances, it can be seen readily that the range of action or effectiveness of the system disclosed may be reasonably large. With a relatively high voltage of 10,000 volts existing between antenna I51 and ground I58, with the o antenna roughly '75 feet high and its capacity to ground being of the order of 500 micromicrofarads, and the radius of the disturbing body approximately three feet and the sensitivity of the amplifier represented being of the order of 0.1 mv., it will be evident that from these assumed values the radius of effectiveness of the system to distinguish or determine disturbing factors coming within the field of the antenna is of the order of feet. This radius may be increased, for instance, by increasing any of the factors hereinabove noted or by increasing the sensitivity of the amplifier.

Under some circumstances it is desirable to shield certain portions of the system from influence of disturbing motions and the like. For this particular purpose, the schematic illustrations of Fig. 13 indicate still another shield electrode I1I as interposed between the antenna I51 and ground I58. The shield electrode connects to ground by Way of the connector I12, which connecting element may, for instance, be the outer shield of a coaxial cable of which the inner element I62 feeds energy to antenna I51. Under the circumstances, any object between the grounded auxiliary shield electrode and ground will have no effect upon the system due to the shielding effect of the element I1I.

The modification disclosed by Fig. 14 is, in many respects, closely related to that hereinabove described in connection with Fig. 13, except that the system is fully insulated from ground.

Referring now particularly to Fig. 14, it may be assumed that the complete assembly included within the housing element I88 is carried particularly upon an airplane, so that a measurement of the elevation of the aircraft relative to ground I58 may easily be determined. Still further, the housing I80, for all practical purposes, may be regarded as the metallic body of the aircraft itself where there is provided an antenna I8I, or other suitable form of electrode element, such as a screen or a metal coating, electrically insulated from the ship housing proper or, in the case of Wood airplane construction, it is formed as a metal coating on the outer surface thereof. 

